1. Field of the Invention
The present invention relates to a V-type engine in which oil separation chambers are provided at upper portion of cylinder heads.
2. Description of the Related Art
In passenger vehicles (or vehicles), a V-type engine is mounted in an engine compartment since it has the advantage that it can be easily mounted although it is a multiple cylinder engine.
The V-type engine is comprised of a cylinder block in which deck cylinder parts are formed on a crankcase in a manner being protruded in V shape, and cylinder heads provided in the respective deck cylinder parts. The reciprocating motion of pistons within cylinders of the respective deck cylinder parts realizes a combustion cycle comprised of an intake stroke, a compression stroke, an explosion stroke, and an exhaust stroke, so that power generated by the pistons can be output from a crankshaft to outside.
In this V-type engine, a crankcase emission control system is used to cause blow-by gas generated inside the V-type engine to flow back so that the blow-by gas may be combusted in each cylinder. On this occasion, if oil content (lubricating oil) in the blow-by gas is combusted, it affects the treatment of exhaust gas, and increases the consumption of lubricating oil. To address this problem, the V-type engine is constructed such that oil separation chambers are provided at upper portion of cylinder heads in at least one of cylinder banks. In general, the oil separation chambers are incorporated in ceilings of rocker covers; if the rocker covers are mounted on the cylinder heads, the oil separation chambers may be mounted at upper portion of the cylinder heads.
By the way, the V-type engine has been required to improve the capability of the oil separation chambers so as to e.g., reduce the consumption of lubricating oil and purify exhaust gas.
For that purpose, the capacity of the oil separation chambers is required to be increased. The V-type engine, however, is mounted in the engine compartment which is limited in space, and hence the total height thereof can be increased only within a limited range. Furthermore, intake manifolds are tightly arranged within the right and left banks constituted by the V-shaped deck cylinder parts, and considering that the V-type engine is transversely mounted, a space outside the right and left banks is also limited (since interference with peripheral equipment should be prevented).
On the other hand, regarding the V-type engine, the technology in which the axes of cylinders are offset from the center of a crankshaft has been proposed to make the engine compact as a whole. According to this technology, the axes of cylinders in respective banks are offset from the center of the crankshaft in the rotational direction of the crankshaft, and the banks are drawn along the axes of the cylinders to the center of the crankshaft, so that the distance between the center of the crankshaft and the bottom surfaces of the cylinders in the banks (i.e., the level of the cylinder surface) can be reduced to make the V-type engine compact (refer to Japanese Laid-Open Patent Publication No. 3-281901, for example).
However, if the banks are drawn along the axes of the cylinders to the center of the crankshaft, it is necessary to greatly modify many parts of an engine. Moreover, if the banks are drawn to the center of the crankshaft, the lower surfaces of the cylinders in one bank may enter into the cylinders in the other bank and interfere with connecting rods of the bank, and some measures must be taken to address this problem.
For this reason, the above technology has the problem that the V-type engine is considerably complicated in structure and requires high cost.